The goal of this work is to determine the structural organization of the individual globin genes in chromatin. The following questions are under direct investigation: 1) Are there detectable structural differences between expressed and non-expressed globin genes in chromatin from erythroid cells? 2) What are the changes in chromatin structure which accompany the developmental sequences characteristic of erythroid maturation in normal and transformed mouse Friend erythroleukemia cells in culture? and 3) What is the component in chromatin (e.g. non-histone protein, modified histone, etc.) which underlies the structural features of the individual globin genes? Currently pancreatic DNase I is used as a probe of chromatin structure since transcriptionally active genes have been shown to be exquisitely sensitive to brief exposure of nuclei to this enzyme. In vitro transcription of isolated chromatin by RNA polymerase has also been used as a probe of the configuration of globin genes.